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At least 1,225 records · Page 68Linked to original sources
PubMed2002

Topological jamming and the glass transition in a frustrated system.

The relationship between extended structures, glassy dynamics and an underlying critical point is examined in the context of a lattice model of fluctuating lines. Monte Carlo simulations are used to construct an effective, coarse-grained dynamics for the "order parameter" near the critical point. Analysis of the effective dynamics reveals that the critical point is associated with diverging barriers leading to the observed Vogel-Fulcher divergence of the relaxation times. A direct connection is established between the presence of extended structures and the activated dynamics.

Journal Article↗
PubMed2004

Frustrated rotations in nematic monolayers.

Tabe and Yokoyama found recently that the optical axis in a chiral monolayer of a ferronematic rotates when water evaporates from the bath: the chiral molecules act as propellers. When the axis is blocked at the lateral walls of the trough, the accumulated rotation inside creates huge splays and bends. We discuss the relaxation of these tensions, assuming that a single dust particle nucleates disclination pairs. For the simplest geometry, we then predict a long delay time followed by a non-periodic sequence of "bursts". These ideas are checked by numerical simulations.

Journal Article↗
PubMed2006

Frustrated structure of an anticlinic-like smectic-C phase.

We present a polarising optical microscopy study of the low-temperature anticlinic-like tilted mesophase of the liquid-crystal compound octylphenyl-2-chloro-4-(p-cyano-benzoyloxy) (DB8Cl). This mesophase has been described as a bilayer smectic structure in which the molecules within each layer are organised in an anticlinic way. The optical textures observed in samples with planar orientation show a double stripe pattern, with the lines aligned parallel to the rubbing direction, characteristic of a double periodic modulation of the refractive index of the material. The long-period modulation is temperature dependent and disappears for thin sample cells (< 5 microm). The short-period modulation is nearly independent of the thickness of the cells. The experimental results are analysed in terms of a model which considers that there is a special distribution of the principal optical axis which may be in or out of the polariser-analyser plane. The observed periodic variation of the principal optical axis could not be interpreted in terms of the original structure proposed for this phase. DB8Cl presents a structure formed by dimers that can be viewed as flexible bent-core-like molecules, showing similarities with phases found in banana-like systems, but exhibiting a much more complex structure.

Crystallization↗
PubMed2001

Historical perspective on airway smooth muscle: the saga of a frustrated cell.

Despite the lack of a clearly defined physiological function, airway smooth muscle receives substantial attention because of its involvement in the pathogenesis of asthma. Recent investigations have turned to the ways in which the muscle is influenced by its dynamic microenvironment. Ordinarily, airway smooth muscle presents little problem, even when maximally activated, because unending mechanical perturbations provided by spontaneous tidal breathing put airway smooth muscle in a perpetual state of "limbo," keeping its contractile machinery off balance and unable to achieve its force-generating potential. The dynamic microenvironment affects airway smooth muscle in at least two ways: by acute changes associated with disruption of myosin binding and by chronic changes associated with plastic restructuring of contractile and cytoskeletal filament organization. Plastic restructuring can occur when dynamic length changes occur between sequential contractile events or within a single contractile event. Impairment of these normal responses of airway smooth muscle to its dynamic environment may be implicated in airway hyperresponsiveness in asthma.

Animals↗
PubMed2004

Expanding applications of the access sheath to ureterolithotripsy of distal ureteral stones. A frustrating experience.

OBJECTIVE: Distal ureteral stones are routinely managed with semirigid ureteroscopy without the need for ureteral dilatation, but some conditions, e.g. large stone burden or difficult catheterization of the ureteral meatus, are time-consuming and would require a tool to facilitate multiple insertions of the ureteroscope and to avoid ureteral injury. An access sheath is now available and it facilitates ureteroscopy of the upper ureter. To answer the question whether its application could be expanded to the distal ureter is the aim of our paper. PATIENTS AND METHODS: 12 distal ureteral stone patients, 8 with stone size >1 cm and 4 with a large prostate, underwent ballistic ureterolithotripsy with the aid of the Access Sheath. The results of the procedure were compared to a second group of 16 patients from our archives. RESULTS: There was no significant difference in operating time and stone-free rate. Although no complications were related to the ureteroscopy, in 42% (5 patients) of the access group the procedure could be completed only after removing the sheath. CONCLUSION: The Access Sheath does not improve the results of the semirigid ureteroscopy of difficult stones in the distal ureter.

Adult↗
PubMed2006

Noncompaction in Duchenne muscular dystrophy: frustrated attempt to create a compensatory left ventricle?

The histological workup of the myocardium of a patient with Duchenne muscular dystrophy and left ventricular hypertrabeculation/noncompaction (LVHT) revealed an extremely thin left ventricular wall and a noncompacted layer double in size compared to the compacted layer. Within the compacted layer islets of fibrous tissue predominated, surrounded by areas of myxoid appearance hardly producing collagen, and occasionally normal or dystrophic cardiomyocytes. The noncompacted layer consisted largely of intact cardiomyocytes rarely intermingled with collagen-producing, fibrous tissue. This variant appearance of the compacted and noncompacted layer was found in all areas of noncompaction. These histopathological findings suggest that LVHT represents a compensatory attempt to overcome the failing compacted but dystrophic myocardium.

Adult↗